(a) Lands not withdrawn from leasing
Upon the expiration of the initial five-year term of any noncompetitive oil or gas lease which was issued prior to September 2, 1960, and which has been maintained in accordance with applicable statutory requirements and regulations, the record titleholder thereof shall be entitled to a single extension of the lease, unless then otherwise provided by law, for such lands covered by it as are not, on the expiration date of the lease, withdrawn from leasing. A withdrawal, however, shall not affect the right to an extension if actual drilling operations on such lands were commenced prior to the effective date of the withdrawal and were being diligently prosecuted on the expiration date of the lease. No withdrawal shall be effective within the meaning of this section until ninety days after notice thereof has been sent by registered or certified mail to each lessee to be affected by such withdrawal.

(b) Known and unknown geologic structures of producing fields
As to lands not within the known geologic structure of a producing oil or gas field, a noncompetitive oil or gas lease to which this section is applicable shall be extended for a period of five years and so long thereafter as oil or gas is produced in paying quantities. As to lands within the known geologic structure of a producing oil or gas field, a noncompetitive lease to which this section is applicable shall be extended for a period of two years and so long thereafter as oil or gas is produced in paying quantities.

(c) Application requirement
Any noncompetitive oil or gas lease extended under this section shall be subject to the rules and regulations in force at the expiration of the initial five-year term of the lease. No extension shall be granted, however, unless within a period of ninety days prior to the expiration date of the lease an application therefor is filed by the record titleholder or an assignee whose assignment has been filed for approval or an operator whose operating agreement has been filed for approval.

(d) Commencement of actual drilling operations
Any lease issued prior to September 2, 1960, which has been maintained in accordance with applicable statutory requirements and regulations and which pertains to land on which, or for which under an approved cooperative or unit plan of development or operation, actual drilling operations were commenced prior to the end of its primary term and are being diligently prosecuted at that time shall be extended for two years and so long thereafter as oil or gas is produced in paying quantities.